This invention relates generally to medical imaging systems, and more particularly, to methods and systems for calibrating X-ray medical imaging devices.
Diagnostic medical imaging requires accurate positioning of imaging equipment in relation to a patient. Further, proper calibration of the diagnostic medical imaging equipment is also required. Some diagnostic medical imaging systems are capable of movement, for example, from one room to another. For example, X-ray systems having wheels or other similar members for moving the system are known.
Distortions within an X-ray diagnostic medical imaging system may be caused by the X-ray system geometry, such as the geometry of an image intensifier. These distortions are static and may be corrected using, for example, models instead of calibration methods as are known. Such distortion may include, for example, pin cushion distortion caused by the curved surface of the image intensifier. Further, dynamic distortion of an X-ray image produced by such a system may be caused by interaction of the earth's and external magnetic fields with the electron paths within the image intensifier resulting in S-distortion. For example, these external distortions may be caused by surrounding factors such as structural elements (e.g. I-beams) carrying magnetic fields, other diagnostic medical imaging equipment operating nearby, such as, for example a magnetic resonance imaging (MRI) system and/or any other external source that may result in a change of the magnetic field surrounding the diagnostic medical imaging system.
For mobile X-ray systems, the dynamic nature of the distortion caused by the magnetic fields cannot be corrected through a static calibration. For example, when moving a mobile X-ray diagnostic medical imaging system from one room to another, non-uniform magnetic fields affecting the system may change.
Known methods provide for distortion correction of diagnostic medical imaging systems. For example, it is known to shield the image intensifier to minimize distortion. Other methods are known that provide active feedback to null out the earth's magnetic fields around the image intensifier using a sensor to measure the magnetic field and correct for changes in the magnetic field around the image intensifier. For fixed systems, other methods are known for measuring the magnetic fields off line and compensating for the magnetic field one time.
These known methods and systems for calibrating and/or correcting for distortion may have undesirable impacts or limitations. For example, shielding in the image intensifier may partially block x-rays being measured and result in a need for higher x-rays doses to image a patient. Further, active feedback is limited to providing correction for changes in a uniform or near uniform magnetic field depending on the number of sensors used. Additionally, off line measurements cannot correct for time varying magnetic fields relative to the x-ray system, such as are caused, for example, when the x-ray system is moved from one room to another.